An idle controller is available for internal combustion engines which, for example, in an idle operating state of the engine, corrects an actual speed against a setpoint speed and for this purpose predefines an indicated setpoint torque.
The indicated setpoint torque is the torque to be generated by the engine at the crankshaft. In the case of a spark ignition engine having homogeneous formation of the fuel/air mixture, the indicated setpoint torque is implemented as a manipulated variable via the engine's air charge. In the case of a spark ignition engine having heterogeneous formation of the fuel/air mixture, or of a diesel engine, the indicated setpoint torque is implemented as a manipulated variable via the fuel quantity. A setpoint value assigned to the indicated setpoint torque is predefined for the manipulated variable used.
In the above cases, the limited air supply to the engine represents the control limit of the idle controller. For this purpose, in the case of a spark ignition engine, a throttle valve in the air intake can be opened to the maximum degree possible. In the case of a diesel engine, the quantity of fuel to be injected can be increased only as far as a value which correlates with the unthrottled air charge. Beyond that point, exhaust gas opacity initially increases to unacceptable levels, and further increase of the injected fuel mass will give no further gain in torque because the calorific value of the mixture does not increase any further.
Stabilization of idle speed may have a particularly marked impact on comfort, in particular when maneuvering at low speeds. In particular with vehicles where the engine has been downsized, for example through the use of an exhaust gas turbocharger or a compressor, the idle controller's maximum usable torque is restricted as a result of the significantly reduced engine displacement. At higher elevations above sea level, having a correspondingly lower ambient pressure, these aspects are restricted even further.